The serving size for boneless skinless chicken breasts is 4 ounces uncooked. It is the same for tenderloins (they have less fat) and most meats are based on 4 ounces although I have seen some at 2 and some at 3.
Normally I make an entire broiler pan and this weekend I cooked 66 ounces of raw chicken that yielded 38 ounces cooked. You have to use the uncooked weight. You can enter fractions of a serving size on here. What I did to make it easier was I divided the 6 total breasts and figured each one is 2.75 servings (on average). As I eat each one I just record 2.75 servings as I figure it will even out in the long run.
Another trick I learned is to buy a weight of whatever meat you are buying that is easily divisible by the serving size. If you buy chicken breasts buy a package with a weight easily divisible by 4 ounces.
Pain is a by-product of a good time.